This project develops molecular Bioprobes that can be introduced into Drosophila neurons. These Bioprobes are designed to reveal dynamic signal integrations within an individual neuron in situ. During the initial grant period, the project develops new FRET (fluorescent resonance energy transfer)-based nano-scale Bioprobes to study Cdc42 signaling at the onset of dendrogenesis. The molecular mechanisms of dendrogenesis are not well understood. The complexity among cells and molecules in the CNS requires an approach that supports high-resolution analysis. Recent advances in genetically encoded Bioprobes allow an unprecedented opportunity to launch this new study. Preliminary observations lead to the hypothesis that spatiotemporal integration of Cdc42 activation and effector availability accounts for the precise space-time at which dendrogenesis initiates in neuron in vivo. Therefore, the goal for the initial grant period is two-fold: (1) to examine the role of Cdc42 signaling at the onset of dendrogenesis, and (2) to demonstrates the power of a Bioprobe-assisted in vivo approach. The Bioprobe-assisted analysis is readily applicable to studies on various properties of a neuron and its compartments.